Conventionally, drip irrigation systems have been employed to supply water or irrigation liquid such as liquid fertilizer to the plants to be grown on the soil in the agricultural land, plantation and the like.
Such a drip irrigation system comprises for example a channel terminal and an elongated drip watering tube connected to the channel terminal, wherein the channel terminal comprises a filter, a fertigation apparatus (a chemigation apparatus if necessary), a back flow prevention apparatus, a main pipe, and the like connected in sequence on the downstream side of a pump that brings up water from a water source. The drip watering tube is laid on the soil on which plants may be grown.
The drip watering tube has a plurality of ejection ports provided to an elongated tube main body at a predetermined interval between the adjacent ports along the longitudinal direction of the tube main body. The irrigation liquid in the tube main body is ejected at a predetermined ejection amount per unit time (or ejection speed) from the ejection ports. Thus, the irrigation liquid is slowly supplied to the soil outside of the drip watering tube (that is, drip irrigation is performed).
The drip watering tube can save water and fertilizer. Further, the drip watering tube can supply water at a moderate supply speed, and oxygen for plant roots can be ensured in the soil. Accordingly, plants can be favorably managed for growing.
In the above drip watering tube, a plurality of drippers, which correspond to the respective ejection ports, for controlling the amount of the irrigation liquid to be ejected from the respective ejection ports per unit time are provided.
The dripper is configured, for example, such that water flowing in the tube main body flows into the dripper through an inlet of the dripper and flows through a pressure reduction channel, which is called labyrinth, in the dripper to reduce the pressure of the water, and is ejected from the ejection port communicated with the pressure reduction channel on the downstream side thereof.
Further, there are known some conventional drippers provided with a so-called differential pressure control mechanism (pressure correction function). Such conventional drippers have, for example, a three-component structure in which an elastic film (for example, silicone rubber) such as a diaphragm is sandwiched by an inflow side member and an ejection side member, as disclosed in PTL 1.
The dripper disclosed in PTL 1 controls the opening/closing of the entrance port of the dripper and the flow rate of water from the exit port of the dripper, by the movement of the diaphragm (film) in accordance with a water pressure outside of the dripper (in-pipe water pressure).
Specifically, in the dripper disclosed in PTL 1, when the in-pipe water pressure outside of the dripper is increased to a certain level, the diaphragm that is originally so disposed as to shield the entrance is deflected by the in-pipe water pressure toward the outlet. Due to the deformation of the diaphragm, the entrance is opened. When the in-pipe water pressure is further increased, the amount of the deflection of the diaphragm toward the outlet is increased. In association with the deformation of the diaphragm, the sectional size of the channel at the outlet is reduced, and thus the ejection amount of water is regulated.
As disclosed also in paragraph [0004] of PTL 1, the dripper disclosed in PTL 1 is designed such that the ejection speed from the dripper has substantially no relation with the fluctuation in pressure of the supplied liquid for irrigation to the dripper.
Therefore, PTL 1 discloses that the disclosed dripper is favorable for limiting variation in the ejection amount of the irrigation liquid between the drippers disposed on the upstream side (high pressure side) and on the downstream side (low pressure side) in the tube main body, to thereby uniformize the growing of plants over the entire soil.